Setting accelerator for binders based on calcium sulfate

Abstract

A method for making a setting accelerator, especially for binders based on calcium sulfate, wherein gypsum together with at least one polycarboxylate is subjected to a dry grinding.

What is claimed is: 
     
       1. A method for making a setting accelerator suitable for binders based on calcium sulfate, the method comprising subjecting materials consisting of gypsum together with at least one polycarboxylate to a dry grinding,
 wherein the polycarboxylate is used in a fraction of 0.05 to 2 wt. % with respect to the gypsum, 
 wherein the polycarboxylate comprises: 
 a) a molar parts of a structural unit S1 of formula (I): 
 
       
         
           
           
               
               
           
         
         b) b molar parts of a structural unit S2 of formula (II): 
       
       
         
           
           
               
               
           
         
         c) c molar parts of a structural unit S3 of formula (III): 
       
       
         
           
           
               
               
           
         
         d) d molar parts of a structural unit S4 of formula (IV): 
       
       
         
           
           
               
               
           
         
         where 
         M independently of each other represents H + , an alkaline metal ion, alkaline earth metal ion, a divalent or trivalent metal ion, an ammonium ion or an organic ammonium group, 
         each R u  independently of the others stands for hydrogen or a methyl group, 
         each R v  independently of the others stands for hydrogen or COOM, 
         m=0, 1 or 2, 
         p=0 or 1, 
         R 1  and R 2  independently of each other stand for a C 1  to C 20  alkyl group, cyclo-alkyl alkylaryl group [AO] n —R 4 , 
         where A=C 2  to C 4  alkylene, R4 stands for H, a C 1  to C 20  alkyl group, cyclohexyl group or alkylaryl group, 
         and n=2−250, 
         R 3  independently of each other stand for NH 2 , —NR 5 R 6 , —OR 7 NR 8 R 9 ,
 where R 5  and R 6  independently of each other stand for a C 1  to C 20  alkyl group, cycloalkyl group, alkylaryl group or aryl group, 
 
         or for a hydroxyalkyl group or for an acetoxyethyl (CH 3 —CO—O—CH 2 —CH 2 —) or for a hydroxy-isopropyl (HO—CH(CH 3 )—CH 2 —) or for an acetoxyisopropyl group (CH 3 —CO—O—CH(CH 3 )—CH 2 —); 
         or R 5  and R 6  together form a ring of which nitrogen is a part, in order to make up a morpholine or imidazoline ring; 
         R 7  is a C 2  -C 4  alkylene group, 
         R 8  and R 9  independently of each other represent a C 1  to C 20  alkyl group, cycloalkyl group, alkylary group, aryl group or a hydroxyalkyl group, 
         and where a, b, c and d represent molar fractions of the respective structural units S1, S2, S3 and S4, wherein 
         a=0.1−0.9, 
         b=0.1−0.9, 
         c=0−0.8, 
         d=0−0.8, 
       
       and provided that a+b+c+d=1. 
     
     
       2. The method according to  claim 1 , wherein the gypsum is ground to a d 50  value of the particle size in the range of less than 100 μm. 
     
     
       3. The method according to  claim 1 , wherein the polycarboxylate is in a solid state of aggregation. 
     
     
       4. The method according to  claim 1 , wherein the polycarboxylate is a comb polymer which has a polycarboxylate backbone and polyether side chains, wherein the polyether side chains are bound by ester, ether and/or amide groups to the polycarboxylate backbone. 
     
     
       5. The method according to  claim 1 , wherein the polycarboxylate satisfies at least one of the following conditions a) to e):
 a) the residues Ru and Rv stand for hydrogen, 
 b) m=0, 
 c) p=1, 
 d) R 1  and R 2  , each independently of the other, stand for -[AO] n —R 4  with n=20-70, 
 e) R 4  represents a methyl group. 
 
     
     
       6. The method according to  claim 1 , wherein the dry grinding occurs in grinding media mill. 
     
     
       7. The method according to  claim 2 , wherein the gypsum is ground to a d 50  value of the particle size in the range of less than 70 μm. 
     
     
       8. The method according to  claim 7 , wherein the gypsum is ground to a d 50  value of the particle size in the range of less than 40 μm. 
     
     
       9. The method according to  claim 1 , wherein the polycarboxylate is used in a fraction of 0.2-1 wt. %. 
     
     
       10. The method according to  claim 1 , wherein the polycarboxylate is in the form of a powder. 
     
     
       11. The method according to  claim 1 , wherein
 a=0.3−0.9, 
 b=0.1−0.7, 
 c=0−0.6, 
 d=0−0.4, 
 
       and provided that a+b+c+d=1. 
     
     
       12. The method according to  claim 1 , wherein
 a=0.5−0.9, 
 b=0.1−0.3, 
 c=0.001−0.005, 
 d=0, 
 
       and provided that a+b+c+d=1. 
     
     
       13. The method according to  claim 6 , wherein the grinding media mill is a ball mill. 
     
     
       14. The method according to  claim 1 , further comprising adding the setting accelerator to a binder based on calcium sulfate, wherein the binder based on calcium sulfate includes at least 90 wt. % of calcium sulfate hemihydrate and/or anhydrite.